| Network Working Group | M. Blanchet |
| Internet-Draft | Viagenie |
| Intended status: Informational | July 2012 |
| Expires: December 31, 2012 |
Implications of running Internet over ports 80 and 443
draft-blanchet-iab-internetoverport443-00.txt
Users are often connected to Internet with very few outgoing ports available, such as only port 80 and 443 over TCP. This situation has many implications on designing, deploying and using IETF protocols, such as encaspulating protocols within HTTP, difficulty to do traffic engineering, quality of service, peer-to-peer, multi-channel protocols or deploying new transport protocols. This document describes the situation and its implications.
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A trend started many years ago has been to provide Internet access to end-users with limited outgoing ports. The most constraint but common case is to only have outgoing TCP port 80 and port 443 opened. Port 80 is expected to carry HTTP and some middleboxes in the network may block non-HTTP traffic on that port. Port 443 is often less policed than port 80 based on the assumption that it is carrying encrypted traffic. However, enterprise firewalls sometimes verify the use of TLS/SSL on port 443.
A consequence of this trend is that Internet statistics show [Labovitz] that a majority of the Internet traffic is over port 80 and 443. And the concentration on these ports are further increasing every year.
While the purpose of this document is not to find or judge the reasons why providers (in the large sense of providing) are blocking all outgoing ports except very few, a few known reasons can be listed, while no opinion on the validity is expressed:
A consequence for the enterprise or non-HTTP application service provider is that there are very few ways to offer a service to its end-users. For example, an application (VoIP, ssh, jabber, ftp, ...) provider need to use an additional IP address and to bind its application server to the port 443 to make sure its users can reach it whatever the characteristics of the access network the nomadic users are attaching to. The other way is to build a tunnel such as VPN to the service infrastructure and then tunnel all application traffic to that tunnel. Obviously for the same reason, the tunnel server itself has to be bound on port 443.
From the application developer point of view, HTTP framework is often chosenfor its own benefits with or without the limited outgoing ports deployment considerations, as discussed in [I-D.tschofenig-post-standardization].
This document uses the term provider in a large sense of some organization offering the Internet access to users. For example, a provider in this document includes coffee shop wifi access, guest access in various public places and networks, hotel networks, enterprise guest access networks, as well as traditional providers such as broadband, mobile and wifi network established large providers.
This section lists some implications of this situation.
IETF provided guidance about the use of HTTP and port 80. For example, [RFC3205] recommended to use different ports than 80 for new services, even when HTTP encapsulation was used. This guidance may need to be revisited.
This situation further complicates the Internet transparency, end-to-end and hourglass model, as discussed in [RFC2775],[RFC3234] and [RFC4924].
If all traffic goes over one or two ports, then it is more difficult to differentiate delay sensitive traffic to bulk traffic while applying policies on forwarding engines at the transport level. The policing nodes on the network haveto open the application payload. For example, for Motion-JPEG over http, parsing the HTTP headers is needed to discover that this data is streaming.
If port 80 and 443 are the only ports opened, then given that middleboxes in networks are inspecting packets and validate HTTP traffic, then a new protocol not based on HTTP and requiring a different transport port or protocol is difficult, while impossible, to deploy as is.
Another consequence of this situation is that protocols and data go over HTTP. HTTP is defined with a specific set of requirements and is implemented in a solution set that is far from the IP layer. It uses TCP transport, has multiple ascii headers in the payload to be parsed, has state, etc. However, the HTTP protocol is being revised [RFC6455][httpbis] related to some of these new requirements.
If an organization has N different services where each one takes a different port, then, in the context of its users only able to use outgoing port 80/443, the organization has to use N IP addresses, one for each service and bind the service on port 443 (or 80) on that IP address. Therefore, the organization increases the rate of its usage of IP addresses. Since IPv4 addresses are almost exhausted, this situation adds pain to the IPv4 address exhaustion. IPv6 addresses are almost limitless to this issue, but having too many IPv6 addresses on the same server to support the services add complexity to the operations.
As a network operator likes to monitor traffic to engineer and troubleshoot the network, it cannot do anymore by only looking at the ports used by the traffic. For example, a peak traffic from a source node that always uses a single outgoing port for all its traffic, may be a video call or video streaming or file copy or a virus related traffic or torrent or ... Therefore, the network operations is blind to what the traffic is, unless the monitoring is at done within the application payload.
A good example of limitations to deploy applications and protocols are IP cameras. These devices send video streams to outside. While a typical protocol stack would use RTP/RTSP for this purpose, often the only way to successfully send the stream in all cases is to encapsulate it over HTTP using Motion JPEG or other coding over HTTP. Similar issues also happen for interactive applications. The constraint of the transport protocol to use may have an important impact on the application design and behavior.
From the application developer point of view, the most garanteed way to get its outgoing traffic from the client host to the Internet (servers) is to carry its application data and protocols over HTTP over port 80 and/or 443. This is, whatever the type of traffic, such as gaming, voice, video, file transfer, augmented reality, 3D, ..., with a wide set of different characteristics. Within the HTTP framework, the Websocket Protocol[RFC6455] is one way to support the variety of applications over HTTP.
Skype is a good illustration of a deployable application that works in most cases. Analysis of Skype behavior [ColumbiaSkype] shows Skype is trying to open outgoing ports, and when not possible, defaults to port 80 or 443 as last resort. Therefore, this illustrates that a successful deployable application should use similar techniques with the last resort being port 80 or 443. That also means the other peer of the communication must be bound to the same 80 or 443 port. This application behavior may require to have standardized ways of handling encapsulation over 80/443 for realtime applications.
Written differently, this situation can be described as the Internet can only run with a single transport protocol(TCP) and two transport ports(80,443). Given that some deployments have HTTP-aware middleboxes on those ports, then the Internet can only run "reliably" over a single transport protocol (HTTP) and a single transport port (443).
Given above, should the IETF only design protocols over HTTP? Should all current protocols be redesigned to be carried over HTTP? (more a question to debate than an affirmation...)
For example, 3GPP and MPEG produced the Dynamic Adaptive Streaming over HTTP(DASH) protocol[DASH] where one of the reasons is related to firewalls and NAT traversal. This new protocol is intended to replace the RTSP [RFC2326] protocol.
Websockets[RFC6455] is a standardized way to encapsulate subprotocols within HTTP and therefore multiplexing the various application protocols within HTTP.
[I-D.tschofenig-post-standardization] also discuss about this issue.
IPv6 could be seen as a way to mitigate that problem. As discussed above, the reasons why access providers or enterprises are limiting outgoing ports are not related to IPv4 address exhaustion or IPv4 itself.
However, on the server side of the connections, given the large IPv6 address space available per server, IPv6 could be used to partly mitigate the problem by having, on a single server, each service bound to a different IPv6 address while using the same transport port 80.
This document does not specify a new protocol. However, it does highlight security impacts of the current Internet access.
This document has no actions for IANA.
Dave Thaler, Hannes Tschofenig, Brian Carpenter, Bernard Adoba have provided input and suggestions to this document.